Concomitant to that: if inequality gets bad enough that we do have a plutocratic class that owns the entire planet, it will be a lot cheaper for them to actuall

Concomitant to that: if inequality gets bad enough that we do have a plutocratic class that owns the entire planet, it will be a lot cheaper for them to actually try to fix things here (or at least slow down on the path to catastrophe) than to move to Mars. The Expanse series, despite not being 'hard SF', does explore a bit of the challenges in detail. Mars is too cold and too dead, and Jovian moons are too far from the sun. You can build arcologies or other artificial habitats where life can be sustained, but the supply chain for making sure those habitats stay up will still require Earth. If anything goes wrong, most everything a habitat will die, and you will need another supply of ready humans and plant/animals to repopulate it. If anything goes wrong, you likely will not have a sufficiently self-sustained autarkic supply chain on Mars to bootstrap the process from scratch again, hence Earth. Earth is an 'infinite' (from the POV of a relatively dead place) supply of biodiversity, genes, organics, people, and manufactured goods.